1. Field of the Invention
The present invention relates to a mold fastening device in which metal molds can be opened and closed within a short time, and to a method of controlling the drive motor in the mold fastening device.
2. Description of the Related Art
A mold fastening device is available, in which a toggle mechanism is provided between the rear plate and movable die plate, and an electric motor drives the toggle mechanism, thereby moving the movable die plate and locking the metal molds. In this mold fastening device, the rotational speed of the electric motor is controlled, moving the movable die plate holding the movable metal mold, thereby closing the metal molds. The movable die plate, for example, is accelerated. When the acceleration reaches a prescribed value, the movable die plate is then moved at a constant speed. When the movable die plate arrives at a prescribed position, it is decelerated and stopped at a desired position. Thereafter, the toggle mechanism is further driven to lock the metal molds with a predetermined fastening force. Jpn. Pat. Appln. KOKAI Publication 2003-231162
The distance the movable die plate should move is determined by the size of the molding to produce. The ranges in which the links of the toggle mechanism are moved in predetermined ranges, too. However, the rotational speed of the drive motor is increased or decreased at a certain rate, regardless of the position where the movable die plate stops, opening the metal molds. That is, since the distance the movable die plate moves changes in accordance with the coupling (angle) state of the links, the position at which the movable die plate starts moving changes even if the rotational speed of the drive motor is increased or decreased at a constant rate. Therefore, the movable die plate is accelerated or decelerated at different rates, depending upon the positions where it is located.
This means that the drive motor operates in a region falling outside its maximum torque, and that the movable die plate is accelerated or decelerated at a rate lower than the maximum acceleration or deceleration rate. Hence, the ability the drive motor has is not effectively utilized, inevitably lengthening the time for opening and closing the metal molds.
This invention has been made to solve the problems described above. An object of the invention is to provide a mold fastening device and a method of controlling the drive motor of the device, which can effectively use the maximum torque of the drive motor and can shorten the time for opening and closing metal molds.